1. Field of the Invention
The present invention relates to computer-aided surgery instrumentation and, more particularly, to the calibration thereof.
2. Description of the Prior Art
In computer-aided surgery, it is known to use surgical instruments detectable by positioning systems in order to have an on-screen representation of the instrument with respect to an operated part of a patient's body. It is readily understood that great amounts of precision and accuracy are required in the space positioning of the surgical instruments in order to obtain reliable representation of the operation. A misrepresentation of the instrument with respect to the patient's body may have dramatic consequences and may even be fatal to the patient. Thus, prior to computer-aided surgery, the instruments must be calibrated.
One known method of calibrating is referred to as the axial-conical calibration. This method consists in achieving pre-determined maneuvers with a surgical instrument having detectable devices thereon for it to be located in space by sensors connected to a position calculator. Namely, a first maneuver consists in rotating the surgical instrument with respect to its longitudinal axis, whereby the position of the latter is set. During this rotation, the position calculator receives readings which will allow it to calculate a transform matrix from the positioning system to the axis of the instrument. Thereafter, in a second maneuver, the instrument is rotated according to a conical trajectory having as an apex the working tip thereof. Hence, the positioning system may interpret and find another transform matrix between the positioning system and the tip of the surgical instrument. Although the axial-conical calibration method is simple, the required maneuvers of calibration may take a few minutes to an inexperienced user and the position calculator may require to repeat the maneuvers if they are judged as being unsatisfactory.
Calibration systems having permanently calibrated instruments have been provided in order to avoid lengthy steps of calibration. In such systems, a working field is scanned by sensors connected to a position calculator which recognizes the geometry of a given surgical instrument, whereby it is calibrated.
Precautions must be taken when using permanently calibrated instruments to ensure that these are not altered or damaged, whether it be in pre-surgery sterilization or during surgery. The instruments are subject to frequent manipulations during surgery, and thus, having sensors or detectable devices thereon involves the possibility that the position of these sensors or detectable devices is altered, whereby precision is lost in the space representation of the instrument. In this case, an inventory of equivalent instruments must be on hand during surgery in case of damage or alteration to an instrument. It would thus be desirable to have a calibration system allowing frequent calibrating by its simplicity and its rapidity of execution, to better suit the surgical room environment.